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Heterologous expression of sodium channel mutations in hypokalemic periodic paralysis reveals 2 variants on channel dysfunction. Charge-reducing mutations of voltage sensing S4 arginine residues alter channel gating as typically studied with expression in mammalian cells. These mutations also produce leak currents through the voltage sensor module, as typically studied with expression in Xenopus oocytes. DIIIS4 mutations at R3 in the skeletal muscle sodium channel produce gating defects and omega current consistent with the phenotype of reduced excitability. Here, we confirm DIIIS4 R3C gating defects in the oocyte expression system for fast inactivation and its recovery. We provide novel data for the effects of the cysteine mutation on voltage sensor movement, to further our understanding of sodium channel defects in hypokalemic periodic paralysis. Gating charge movement and its remobilization are selectively altered by the mutation at hyperpolarized membrane potential, as expected with reduced serum potassium.
Figure 1. Closed-state fast inactivation in rNaV1.4 and R3C channels. (A) Steady-state availability: channels were conditioned for 300 ms at voltages from â120 mV to 25 mV, prior to test at â20 mV. Traces show test responses following conditioning at â120 mV (solid line) or â60 mV (dotted line), with voltage dependence below. B. Kinetics of sodium current inactivation; channels were conditioned at voltages from â85 mV to â30 mV for variable duration, prior to test at â20 mV. Traces show responses for selected sweeps up to 25 ms conditioning at â60 mV. Plots of voltage dependence are shown below, with arrows representing fast inactivation ranges of recovery, closed-state entry, and open-state entry for wild type rNaV1.4. Calibration for A, B: vertical 2 μA; horizontal 10 ms. (C, D). Charge movement from experiments as in (B) after block of ionic current with 2 μM TTX. Normalized charge (Q/QMAX) after 300 ms conditioning is shown in (C), with kinetics of charge decrement shown in (D). Values represent mean ± SEM from 10 to 29 (rNaV1.4) or 11 to 32 (rR1128C) experiments.
Figure 2. Charge movement in wild type rNaV1.4 and rR1128C channels. (A) Traces comparing responses at â60 mV and at 0 mV, from a holding potential of â120 mV. Calibration: vertical 100 nA (â60 mV) or 500 nA (0 mV); horizontal 10 ms. (B) Voltage dependence of charge movement (Q/V relation) in response to 20 ms depolarization, from â110 mV to 60 mV. Values represent mean ± SEM from 34 (rNaV1.4) or 18 (rR1128C) experiments.
Figure 3. Recovery and charge remobilization in wild type rNaV1.4 and R3C channels, following closed-state fast inactivation with depolarization to â40 mV. (A) Traces of recovery of ionic current with â90 mV hyperpolarizing commands and test at â20 mV, with voltage-dependence shown at right. (B) Traces and voltage dependence of the slow component of charge remobilization in experiments after TTX block, using 0 mV test. Calibration for traces: vertical 1â2 μA (A), 400 nA (B); horizontal 10 ms. Values represent mean ± SEM from 16 to 21 (rNaV1.4) or 8 to 10 (rR1128C) experiments.
Cannon,
Pathomechanisms in channelopathies of skeletal muscle and brain.
2006, Pubmed
Cannon,
Pathomechanisms in channelopathies of skeletal muscle and brain.
2006,
Pubmed
Cannon,
Voltage-sensor mutations in channelopathies of skeletal muscle.
2010,
Pubmed
Capes,
Domain IV voltage-sensor movement is both sufficient and rate limiting for fast inactivation in sodium channels.
2013,
Pubmed
,
Xenbase
Cha,
Voltage sensors in domains III and IV, but not I and II, are immobilized by Na+ channel fast inactivation.
1999,
Pubmed
,
Xenbase
Chanda,
Tracking voltage-dependent conformational changes in skeletal muscle sodium channel during activation.
2002,
Pubmed
,
Xenbase
Fan,
Transient compartment-like syndrome and normokalaemic periodic paralysis due to a Ca(v)1.1 mutation.
2013,
Pubmed
Francis,
Leaky sodium channels from voltage sensor mutations in periodic paralysis, but not paramyotonia.
2011,
Pubmed
Gosselin-Badaroudine,
Gating pore currents and the resting state of Nav1.4 voltage sensor domains.
2012,
Pubmed
,
Xenbase
Groome,
NaV1.4 mutations cause hypokalaemic periodic paralysis by disrupting IIIS4 movement during recovery.
2014,
Pubmed
Jones,
Biophysical defects in voltage.gated sodium channels associated with long QT and Brugada syndromes.
2008,
Pubmed
Jurkat-Rott,
Pathophysiological role of omega pore current in channelopathies.
2012,
Pubmed
Jurkat-Rott,
Sodium channelopathies of skeletal muscle result from gain or loss of function.
2010,
Pubmed
Männikkö,
Hypokalemic periodic paralysis: an omega pore mutation affects inactivation.
2015,
Pubmed
Sokolov,
Gating pore current in an inherited ion channelopathy.
2007,
Pubmed
,
Xenbase
Sokolov,
Depolarization-activated gating pore current conducted by mutant sodium channels in potassium-sensitive normokalemic periodic paralysis.
2008,
Pubmed
,
Xenbase
Struyk,
Gating pore currents in DIIS4 mutations of NaV1.4 associated with periodic paralysis: saturation of ion flux and implications for disease pathogenesis.
2008,
Pubmed
Sung,
Genotype and phenotype analysis of patients with sporadic periodic paralysis.
2012,
Pubmed
